PAHs: The Indiscriminate and Silent Carcinogens among us


Fig: Burning of garbage can be one of the most potent and common sources of Polycyclic Aromatic Hydrocarbons (Photo by Mark Williams courtesy of

Ever enjoyed a sumptuous meal of roasted meat? It is a delicious and sumptuous delicacy loaded with cancer- causing potential due to the presence of polycyclic aromatic hydrocarbons (PAHs).  Polycyclic Aromatic Hydrocarbons (PAHs) are a class of organic chemical compounds found generally everywhere in the environment. They are polycyclic derivatives of the Benzene ring (a six- carbon hexagonal compound which is cyclic in nature). Some of the most popular PAHs include naphthalene (used in disinfection in toilets) and phenanthrene.  They are usually found in the environment as a result of incomplete combustion of fuel from vehicle engines, incinerators, fossil fuels, forest fires, tobacco smoke and also high temperature cooking of foods such as meat and vegetables.

The International Association for Research on Cancer has classified a number of PAHs as carcinogens or potentially carcinogenic including naphthalene derivatives such as naphthylamines and pyrene derivatives such as benzo-pyrene. PAHs can be inhaled through the air or ingested through foods. They are not completely metabolized in the human body ending up as very reactive species capable of causing mutating changes in the DNA structure resulting into conditions such as cancer. PAHs have been known to be culpable of stomach, skin, lung and liver cancers. Due to their prevalence in everyday life, it is essential to appreciate the routes of exposure to them in order to find ways of minimizing their effects in our lives:


This is the most common way through which PAH exposure takes place. Populations living in urban areas or on the road sides have a high likelihood of exposure to PAHs due to the incomplete combustion of diesel in vehicle exhausts. Many vehicles emit a high amount of PAHs from their exhausts resulting into air pollution and exposing the population around to cancerous risks. Also, forest fires and the usage of fossil fuels such as charcoal for cooking may expose many people especially in the developing nations to higher risks of cancer due to exposure to PAHs. Populations living near industries, especially those using fossil fuels like coal, may also be exposed to high PAHs levels in the environment.

francesco falciani

Fig: Air pollution from industries. A major source of PAHs in urban areas (photo by Francesco Falciani through


Foods such as meats cooked under very high temperatures can result in the formation of several forms of PAHs. When foods are cooked over a low and regulated heat, the disintegration of the organic bonds in the food is gradual resulting into much more tender and healthier foods as opposed to when they are cooked under extremely high heat which results into incomplete breakdown of the chemical bonds in the foods producing some PAHs. Smoked or roasted foods are very big carriers of PAHs and if ingested regularly may increase the chances of development of several kinds of cancers.

marilyn acosta

Fig: Roasted meat on a grill. High temperature cooking methods such as roasting may end up elevating the levels of PAHs in foods leading to more instances of Cancer (Photo by Maryline Acosta through


Tobacco is composed of a cocktail of PAHs. It also contains other cancer causing substances such as Cadmium and benzene derivatives therefore making it one of the most potent causes of cancer of the lungs. Secondary smokers are also at the risk of interacting with the PAHs from tobacco which could result into cancer.

Polycyclic Aromatic Hydrocarbons are very potent carcinogens due to their metabolism in the body. They are usually completely broken down by some animals but are not fully metabolized in Humans leading to the formation of very reactive intermediates in the process. These reactive intermediates can alter the structure of DNA through bonding or transferring of important DNA bases leading to gene mutation and ultimately cancer. Some of the well known potentially cancer-causing PAHs include naphthalene and pyrene derivatives. Some enzymes have however been known to deter the cancer causing effects of these PAHs in a number of cases thus suppressing the occurrence of cancer.

PAHs are environmental pollutants which should be of concern at the local and national level. Monitoring of the levels of PAHs requires the usage of techniques such as liquid chromatography and mass spectrometry. These instruments could be stationed government environmental or quality control labs.

References and further reading


Author: nanosphereblog

John Mmbaga is a graduate of B.Sc (Biochemistry and Chemistry) from Kenyatta University in Nairobi, Kenya. He is currently pursuing an M.Sc in Environmental Chemistry at the University of Nairobi. He has a combined working experience of over 10 years in the Corporate, Non Profit and Agricultural sectors in Kenya, having worked at various positions including but not limited to managerial and business ownership. He also has been a recipient of funding from the National Commission for Science Technology and Innovation (Currently- National Research Fund) in Kenya for his post graduate work on the ‘Design and fabrication of polymer- layered silicate nanocomposites for water remediation’. He has interests in nanocomposite materials for water treatment and purification, electrochemical sensors for water pollutant detection, sensors in medical diagnostics, nanotechnology in energy conversion and applications of nanotechnology in agriculture. He also has attended a short Course on ‘Nanotechnology and Nano-sensors’ at the Technion University, Haifa, Israel among other short courses. He has an immense passion for communicating about nanotechnology and its capacity to solve African developmental problems especially in the fields of Agriculture, Healthcare, Energy and Environmental degradation.

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